This invention relates to areal density in data storage devices and particularly to assigning different a real densities to different recording surfaces of a multi-surface hard disc drive.
Areal data density represents the quantity of data (e.g., number of bits) that may be recorded in a given area of a recording surface. In a disc drive, areal density is a function of the track density, which is the number of tracks per inch (TPI) across the radius of the disc surface, and recording or bit density, which is the number of bits per inch (BPI) recorded along a track.
In the past, the track density was the same for all surfaces of the disc drive. The magnetic heads were manufactured to specifications based on the track density. Specifically, the widths of the read and write portions of the head were designed to not extend to an adjacent track and thus had to be smaller than or equal to the track width associated with the track density.
Like all manufacturing processes, the process for forming a head is susceptible to slight variations that result in heads with nonuniform widths. As the track density increases, these slight variations will cause a greater percentage of heads to fail initial testing because they are unable to meet the track density specification. This increase in failure rate increases manufacturing time and cost.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
A method sets bit densities and track densities for a plurality of heads in a data storage device. The method includes determining an initial bit density value and an initial track density for each head. An initial total capacity for the storage device is determined based on the initial track densities and the initial bit densities. A desired capacity for the storage device is selected and the initial total capacity and the desired capacity are compared. One of either a bit density or track density is then adjusted so that the data storage device has an adjusted capacity that provides some excess capacity over the desired capacity where the excess capacity is less than any excess capacity that was present between the initial capacity and the desired capacity. A data storage device formed through this method is also provided.
Other features and benefits that characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.